Dropdown menu selection uniformity

### Issue Details

There are various ways of showing what is selected is selected in AdGuard DNS's dropdown menu's. The lack of uniformity to show what's selected could be improved.

- The companies page uses a combination of white and blue ticks to show what's selected. This confused me the most as I had to select both options to be sure what the active menu was.

---

- Query type dropdown menus have a single blue tick on what's selected, this is the cleanest way of showing what's selected in my opinion.

---

- The 'all devices' dropdown has blue dots next to each item, I'm not honestly sure what the reason is for showing blue dots next to each item.

---

- The server settings dropdown shows no selection at all, which makes it seem like it's been missed.

---

- The 'check the domain' dropdown highlights the selected item.

### Proposed solution

Use the same method to show what's selected in every dropdown menu. A single blue tick should be fine, there's no need to add additional white ticks and blue dots which add to the confusion of what may be selected.

Alternatively, highlighting the selected item is also a good option as is done with the 'check the domain' dropdown.

### Alternative solution

_No response_